Small diameter high tensile strength coaxial electrical cable



Nov. 28, 1967 COSTLEY ETAL 3,355,544

SMALL DIAMETER HIGH TENSILE STRENGTH COAXIAL ELECTRICAL CABLE Filed Feb. 24, 1965 10 FIG 1 FINE GAUGE HIGH 2 TENSILE STRENGTH ARMOR POLYETHYLENE POLYE TH YL ENE CONDUCTOR ll GRAPHITE I4 2 CONDUCTOR FIG, 2

VIN/fan G. Cosf/eg James E. Coiireil INVENTQRS ATTORNEY.

AGENT.

United States Patent 3,355,544 SMALL DIAMETER HIGH TENSILE STRENGTH COAXIAL ELECTRICAL CABLE Vivian G. Costley, Takoma Park, and James E. Cottrell,

Wheaton, Md., assignors to the United States of America as represented by the Secretary of the Navy Filed Feb. 24, 1965, Ser. No. 435,412 7 Claims. (Cl. 174-106) ABSTRACT OF THE DISCLOSURE A Water tight, low noise, coaxial electrical cable having a overall composite diameter of no greater than approximately 70 mils and a tensile strength in excess of approximately 150 p.s.i. for suspending a hydrophone assembly of a sonobuoy from a float and for transmitting electrical signals from the former to the latter. A solid or stranded annealed copper wire inner conductor having a diameter of approximately 11 mils is surrounded by dielectric insulating material of either polyethylene, polypropylene, or nylon having an outer diameter of approximately 30 mils; an electrically conductive thin film of colloidal graphite having a resistance of 03-500 megohms per foot is deposited on the dielectric. A plurality of strands of annealed copper wire having a diameter of approximately 5 mils are helically wound around the graphite coated dielectric to form the outer conductor. A braided wire armor sheath woven from high strength (in excess of 500,000 p.s.i.), fine gauge (not greater than approximately 5 mils), carbon steel wire surrounds the outer conductor. Lastly, the cable is surrounded by an insulating jacket having a thickness of approximately 4.5 mils of either polyethylene, polypropylene or nylon.

The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.

This invention relates to low noise electrical cables and more particularly to a new and improved coaxial conductor of such construction as to have a small diameter, reasonably low attenuation for a 400 kc. electrical signal, watertight under high hydrostatic pressures and yet being capable of supporting high tensile loads.

One of the most critical problems confronting the designers of electrical cables has been the development of a small diameter cable having a high tensile strength, which problem is solved by the present invention, In conjunction with certain military weapons systems, underwater acoustic listening devices called sonobuoys are planted in the ocean by being dropped from over-passing aircraft. When the sonobuoy package is released from the plane, a parachute deploys and a flotation bag inflates as the sonobuoy descends to the waters surface where, upon impact with the surface of the water, the flotation bag remains on the surface and acts as a floating platform for a radio transmitter while the hydrophone assembly of the sonobuoy continues to descend to a predetermined depth many thousands of feet below the waters surface. As the hydrophone assembly descends, a coaxial electrical conductor is paid out from a coil within the descending structure and when the sonobuoy reaches its predetermined depth, the coaxial conductor not only provides an electrical transmission path between the submerged hydrophones and the floating transmitter but additionally serves as the sole supporting structure for the suspended sonobuoy. Since the sonobuoys are moored many thousands of feet below the waters surface, extensive amounts of cable are required for the mooring of each sonobuoy and in order to store the cable within a package of reasonable size, a cable is desired which has a very small diameter, reasonably good electrical properties, and yet is capable of supporting the suspended sonobuoy. The present invention provides such a coaxial cable having a small diameter, reasonably good electrical properties, a minimum of self generated electrical noise and a high tensile strength, thus enabling an extensive quantity of cable to be stored within a package small enough to maintain the feasibility of the Weapon system.

An object of the present invention is the provision of a multi-conductor electrical cable having a high ratio of tensile strength to cross-section.

Another object is to provide a small-diameter flexible electrical conductor having a high tensile strength and possessing good electrical conductivity.

Other objects and advantages of this invention will hereinafter become more fully apparent from the following description of the annexed drawings, which illustrate a prefer-red embodiment of the invention, wherein:

FIG. 1 is a plan view with adjacent elements cut away to disclose the elements thereunder; and

FIG. 2 is a sectional view taken along line 22 of FIG. 1.

The preferred embodiment of the electrical cable of this invention is shown in the drawings in a highly magnified form to more clearly point out the structural features of the cable. As seen in the drawings, the electrical cable, shown generally at 10, is a coaxial cable having an inner conductor 11 and an outer conductor 12. The center conductor 11 is made of annealed copper and may be either a solid wire, as shown in the drawings, or alternatively a stranded annealed copper wire. Surrounding the center conductor 11 and separating the center conductor from the outer conductor is a body of dielectric material 13. The dielectric body 13 may be made from any suitable material having a low dielectric constant and being substantially incompressible, such as polyethylene, polypropylene, and a modified form of nylon available from the DuPont Corporation under the name of H-film and HF-film, The low noise treatment applied to the outer surface of the dielectric is a thin film 14 of an electrically conductive substance such as a colloidal graphite with a resistance of 0.3 to 50 megohms per foot of cable. The outer conductor 12 is comprised of a plurality of strands of annealed copper wire wrapped in a helix around and over the high-density polyethylene body 13. The electrical cable of this invention is constructed with coaxial conductors to provide for maximum separation of the conductors by the dielectric while maintaining the diameter of the cable at a minimum.

To impart a high tensile strength to the cable while maintaining reasonably good electrical properties and small size, a sheath of armor 15 which is comprised of many strands of high-strength carbon steel wire formed into a braid is applied directly over the outer conductor 12. The wire used in the armor braid 15 is a special highstrength carbon steel wire drawn into a fine gauge and is commercially available from the National Standard Company, Niles, Mich, under the name of Rocket Wire. It has been found that the outer diameter of the cable may be maintained at a minimum while maintaining reasonable electrical properties by using this material which has a tensile strength in excess of 500,000 pounds per square inch. Using this material in a braid on the outer periphery of the cable rather than in the core also enhances the cables electrical properties while maintaining a small outer diameter. Optimum use of the volume occupied by the armor would be made by a tubular structure of the same material from which the wire is produced, however, the high-strength carbon steel utilized to make the rocket wire cannot be fabricated into sufficiently thin tubular forms by known production methods. Therefore, the best possible use of the annular volume occupied by the cable armor 15 can be achieved by using the braided Wire type of armor. The cable may or may not be provided with a thin jacket 16 of polyethylene, nylon, or polypropylene applied directly over the braided armor to confine the radial dimensions of the cable and prevent radial expansion when not under a tensile load.

By way of example, a coaxial cable constructed in the manner shown in the drawings may have an outer diameter of .070 inch and have a tensile strength in excess of 150 pounds. To produce an electrical cable having such specifications, the cable should be provided with a center conductor of annealed copper having a diameter of 11 mils, the center conductor being surrounded by a dielectric material having an outer diameter of 30 mils, the outer conductor being formed of a plurality of strands of fine annealed copper wire having a diameter of mils and being wrapped in a helix around and over the dielectric material, the armor being formed of a highstrength carbon steel Wire of 5 mils diameter braided into a sheath and applied directly around the outer conductor, and an optional protective jacket of 4 /2 mils being applied around the armor braid.

From the foregoing, it may be seen that the particular arrangement of the structural elements of the cable in conjunction with the specific materials used in the elements of the cable cooperate to produce an electrical cable having the optimum mechanical-electrical properties obtainable in a cable of limited diameter, The present invention provides electrical cable having good electrical conductivity with sutficient insulation between the inner and outer conductors being provided by the dielectric body 13. The use of conductive material on the outer surface of the dielectric reduces the self generated cable noise to a minimum. Said cable noise arises when the cable is cycled through a sinusoidal type of tensile loading produced when the flotation bag is vertically displaced by the waves in open ocean. The use of a multi-strand helicallywound outer conductor 12 imparts greater flexibility to the cable than would be the case if the cables outer conductor were constructed of a tubular element. In a similar manner, the braided wire armor not only protects the cable from physical damage and provides the cable with a very high tensile strength, but the armor in the braided form also enhances the flexibility of the cable. The cable of this invention may be made to have a very high tensile strength and yet be of extremely small diameter and exhibit a high degree of flexibility, thus enabling thousands of feet of this cable to be wound in a coil within the confines of a small compartment in a sonobuoy. The coaxial cable of the present invention is not only smaller, stronger, and more flexible than previously known coaxial cables but because of these characteristics, this cable may be used to advantage in many applications and particularly in air-dropped sonobuoys having heavy hydrophones 55 which are suspended by the cable thousands of feet below a floating platform on the ocean.

Obviously many modifications and variations of the present invention are possible in the light of the above teachings. It is therefore to be understood, that within the scope of the appended claims, the invention may be practiced otherwise than as specifically described.

What is claimed is:

5 1. A light weight, small diameter, flexible multi-conductor electrical cable having a high tensile strength comprising an elongated cylindrical body of dielectric material, a first electrical conductor embedded axially within said cylindrical dielectric body,

a second electrical conductor formed on the outer peripheral surface of said dielectric body concentrically about said first conductor,

an armor formed concentrically about said second conductor and in contact therewith,

said armor being formed of a plurality of fine guage, high-tensile strength wires braided into a cylindrical sheath, each of said wires having a diameter of approximately 0.005 inch or smaller and a tensile strength in excess of approximately 500,000 pounds per square inch.

2. The electrical cable of claim 1 further comprising a thin cylindrical jacket concentrically disposed about said armor and contacting said armor.

3. The electrical cable of claim 1 wherein said dielectric material selected from a group consisting of polyethylene and polypropylene,

4. The electrical cable of claim 3 wherein said second conductor comprises a plurality of strands of annealed 30 copper wire wrapped around and over said dielectric body in a helical pattern.

5. The electrical cable of claim 4 further comprising a thin film of colloidal graphite formed on the surface of said cylindrical body of dielectric material for noise suppression.

6. The electrical cable of claim 5 wherein said braided armor comprises a plurality of strands of high-strength carbon steel wire formed into a braid to define a sheath surrounding and contacting said second conductor.

7. The electrical cable of claim 4 wherein said braided armor comprises a plurality of strands of high-strength carbon steel wire applied in a braid to form a sheath surrounding and contacting said second conductor.

References Cited UNITED STATES PATENTS 2,133,863 10/1938 Knoderer 174-106 2,337,556 12/1943 Hosking 174106 X 3,126,358 3/1964 Lemmerich.

3,180,926 4/1965 Trill 174107 OTHER REFERENCES Amphenol Cable-Pay-TV Transmission Cable, Electronics World, vol. 72, N0. 5, November 1964, p. 118.

LEWIS H. MYERS, Primary Examiner.

H HU ER E s i tant Examiner. 

1. A LIGHT WEIGHT, SMALL DIAMETER, FLEXIBLE MULTI-CONDUCTOR ELECTRICAL CABLE HAVING A HIGH TENSILE STRENGTH COMPRISING AN ELONGATED CYLINDRICAL BODY OF DIELECTRIC MATERIAL, A FIRST ELECTRICAL CONDUCTOR EMBEDDED AXIALLY WITHIN SAID CYLINDRICAL DIELECTRIC BODY, A SECOND ELECTRICAL CONDUCTOR FORMED ON THE OUTER PERIPHERAL SURFACE OF SAID DIELECTRIC BODY CONCENTRICALLY ABOUT SAID FIRST CONDUCTOR, AN ARMOR FORMED CONCENTRICALLY ABOUT SAID SECOND CONDUCTOR AND IN CONTACT THEREWITH, SAID ARMOR BEING FORMED OF A PLURALITY OF FINE GUAGE, HIGH-TENSILE STRENGTH WIRES BRAIDED INTO A CYLINDRICAL SHEATH, EACH OF SAID WIRES HAVING A DIAMETER OF APPROXIMATELY 0.005 INCH OR SMALLER AND A TENSILE STRENGTH IN EXCESS OF APPROXIMATELY 500,000 POUNDS PER SQUARE INCH. 